1. Field of the Invention
The present invention relates to a machine tool having a plurality of working regions located adjacent each other, and comprising a movable body such as a spindle head or a headstock which is adapted to move within any one of the working regions in a first machining mode and to move across the plurality of working regions in a second machining mode.
2. Description of the Prior Art
In a vertical machining center of long table type, for example, a partition plate is placed upright at a longitudinally middle position of a long table to split the long table into two working regions in a first machining mode and, when a workpiece is machined in one of the working regions, a set up operation for machining the next workpiece is performed in the other adjacent working region. In a second machining mode, the partition plate is removed, whereby a single working region is provided on the entire long table for machining an elongate workpiece.
The vertical machining center typically includes a saddle movable longitudinally of the long table (along the X-axis) on a bed disposed behind the long table, a column disposed upright on the saddle and movable back and forth (along the Y-axis), and a spindle head provided on a front face of the column and vertically movable (along the Z-axis). A workpiece is machined with the column and the spindle head projecting over the long table.
In the vertical machining center, as described above, the long table is available not only to provide the two working regions separated by the partition plate but also to provide the single working region. Therefore, it is impossible to mechanically limit the movement of the saddle mounted with the spindle head to allow the spindle head to move only within each of the working regions separated by the partition plate, but the saddle is allowed to freely move from one end to the other end of the long table.
Where a workpiece is to be machined in either of the working regions separated by the partition plate in the vertical machining center, the movement of the saddle is controlled on a software basis by an NC apparatus so as to prevent the spindle head (or a spindle head cover) and the column (or a column cover) projecting over the table from colliding against the partition plate when moving along the X-axis.
Further, limit switches, for example, are provided as detection means on opposite sides of the partition plate to prevent the collision of the column, the spindle head and the like against the partition plate which may otherwise result in injury to an operator performing a set up operation in the adjacent working region when the NC apparatus fails to properly control the movement of the saddle under abnormal conditions. When the detection means detects the saddle or the column in an unintended region, a power supply to a servo motor for driving the saddle is forcibly cut off to stop the movement of the saddle.
Even if the power supply to the servo motor is cut off, the saddle does not immediately stop moving, but stops after having moved a certain distance under its own inertia. Therefore, a machining range, i.e., the movement range of the spindle head and the like along the X-axis, is defined in each of the working regions separated by the partition plate in consideration of the coasting distance of the saddle at abnormal stoppage.
Where the long table is split into the two working regions by the partition plate, the machining ranges in the respective working regions in which the spindle head and the like are actually permitted to move along the X-axis are diminished to a certain extent with respect to the entire working regions. If an attempt is made to provide sufficient machining ranges in the respective working regions, on the contrary, the machine tool entirely has a greater size, requiring a greater installation space.
Particularly, where the saddle mounted with the column and the spindle head has a greater weight or a higher rapid traverse rate, the coasting distance of the saddle at the abnormal stoppage is increased. Accordingly, the aforesaid problem is more remarkable.
It is therefore an object of the present invention to provide a machine tool having a plurality of working regions located adjacent each other, and comprising a movable body such as a saddle which is adapted to move within any one of the working regions in a first machining mode and to move across the plurality of working regions in a second machining mode, wherein a machining range to be defined within each of the working regions is maximized without the need for consideration of the coasting distance of the movable body at abnormal stoppage.
In accordance with the present invention to achieve the aforesaid object, there is provided a machine tool, which has a plurality of working regions located adjacent each other, and comprises a movable body adapted to move within any one of the working regions in a first machining mode and to move across the plurality of working regions in a second machining mode, and a stopper which prevents the movable body from moving from the one working region into the other working region in the first machining mode and permits the movable body to move from the one working region into the other working region in the second machining mode.
In the machine tool having the aforesaid construction, the movable body is permitted to freely move across the plurality of working regions in the second machining mode. In the first machining mode, on the other hand, the stopper forcibly prevents the movable body from moving from the one working region into the other working region. This obviates the need for defining a limited machining range in each of the working regions in the first machining mode in consideration of the coasting distance of the movable body at abnormal stoppage as in the conventional machine tool, but makes it possible to define maximum machining ranges in the respective working regions.
Thus, the machine tool provides sufficient machining ranges in the respective working regions, and yet has a compact size. Thus, the installation space of the machine tool can be minimized. Where the movable body has a greater weight or a higher rapid traverse rate and, hence, has a greater coasting distance at the abnormal stoppage, this arrangement is particularly effective.
Where a partition is provided for separating the adjacent working regions from each other in the first machining mode in which the movable body is allowed to move within the one working region, the stopper is preferably adapted to limit the movement range of the movable body to prevent the movable body from colliding against the partition in the first machining mode.
The stopper may comprise a movable stopper member provided in association with the movable body and movable together with the movable body, and a stationary stopper member provided at a fixed position to be brought into abutment against the movable stopper member. In this case, one of the movable stopper member and the stationary stopper member may comprise a base having an opening which allows for passage of the other stopper member, and an open/close mechanism for opening and closing the opening of the base.